Government System — Parliament, President & Administration

Why This Chapter Matters

Biology usually earns the largest share of General Science marks in SSC MTS and CHSL, often 5 to 7 questions, because it covers your own body, common diseases, and the plants and environment around you. This is also the subject where "common sense plus a few precise terms" beats hours of blind memorisation, since you already carry decades of lived experience about how your body works and what makes you fall sick.

The single biggest mistake aspirants make is mixing up which organ or system does which job, especially when two systems sound similar or work close together, like confusing the respiratory and circulatory systems, or mixing up which vitamin deficiency causes which disease. This chapter walks through the human body system by system, then common diseases and prevention, then plants and ecology, always tying the term back to something you have felt or seen, a fever, a vaccination, a garden, a river. Read it once carefully and these become facts you cannot forget, not facts you have to cram the night before.

1. Human Body Systems Simplified

Your body is not one single unit but a group of systems, each with its own job, working together non-stop. SSC tests basic function and key organs of each system, not deep medical detail.

The digestive system breaks down the food you eat into nutrients your body can absorb and use. Food travels through the mouth, food pipe (oesophagus), stomach, small intestine, and large intestine, in that order. In the mouth, teeth crush food and saliva starts breaking down starches. In the stomach, hydrochloric acid and enzymes break down proteins. The small intestine is where most nutrient absorption into the blood happens, aided by bile from the liver and enzymes from the pancreas. The large intestine absorbs water and forms waste, which finally leaves the body.

Exam trap: Students sometimes think the stomach absorbs most nutrients since food spends time there. Absorption of most nutrients actually happens in the small intestine, not the stomach, which mainly handles the early breakdown of proteins.

The respiratory system brings oxygen into your body and removes carbon dioxide. Air enters through the nose, travels down the windpipe (trachea), and reaches the lungs, where it fills millions of tiny air sacs called alveoli. Oxygen crosses into the blood at the alveoli, and carbon dioxide crosses out to be exhaled. An adult at rest breathes roughly 12 to 20 times a minute, and this rate rises sharply during exercise as the body demands more oxygen.

The circulatory system transports blood, carrying oxygen, nutrients, and waste, throughout your body. The heart is the pump at the centre of this system, a muscular organ roughly the size of your own fist, beating about 60 to 100 times per minute at rest. It has four chambers, two upper (atria) and two lower (ventricles), and it pumps blood through two loops: one to the lungs to pick up oxygen, and one to the rest of the body to deliver that oxygen. Blood travels through three types of vessels: arteries carry blood away from the heart, veins carry blood back toward the heart, and capillaries are the tiny vessels connecting the two, where the actual exchange of oxygen and nutrients with body tissue happens.

Memory hook: Remember artery direction with "Arteries Away" — both start with A, and arteries always carry blood away from the heart. Veins do the opposite, carrying blood back home.

Human blood itself has four components. Red blood cells (RBCs) carry oxygen using a protein called haemoglobin, which is exactly what gives blood its red colour. White blood cells (WBCs) are your body's defence force, fighting infections and foreign invaders. Platelets help blood clot, stopping bleeding when you get a cut. Plasma is the pale yellow liquid part of blood that carries all these cells along with nutrients and waste around the body.

Exam trap: A very common SSC question asks which blood component fights infection. The answer is white blood cells, not red blood cells, which are strictly for carrying oxygen. Keep this pairing clear: Red for oxygen, White for defence.

The nervous system is your body's communication and control network, made up of the brain, spinal cord, and nerves spreading throughout the body. The brain is the control centre, generally divided into three main parts for exam purposes: the cerebrum (largest part, responsible for thinking, memory, and voluntary movement), the cerebellum (controls balance and coordination), and the medulla oblongata or brainstem (controls involuntary, life-sustaining functions like heartbeat and breathing, functions you never consciously think about). The spinal cord runs down your back inside the spine and relays messages between the brain and the rest of the body, and it also handles quick automatic reactions called reflex actions — pulling your hand back instantly from a hot pan happens through the spinal cord acting before your brain has even fully registered the pain, which is exactly why you react so fast.

The skeletal system gives your body its frame, protects internal organs, and works with muscles to allow movement. An adult human body has 206 bones. The skeleton also produces blood cells inside bone marrow and stores minerals like calcium.

Exam trap: Newborn babies actually have around 300 bones, more than adults, because several small bones gradually fuse together as a child grows into adulthood, settling at 206. If a question asks about a newborn's bone count specifically, remember it is higher than the adult figure, not lower.

The muscular system works with the skeleton to produce movement. Muscles are broadly of three types: skeletal muscles (attached to bones, under your voluntary control, used for walking or lifting), smooth muscles (found in organs like the stomach and intestines, working automatically without conscious control), and cardiac muscle (found only in the heart, working automatically and tirelessly your entire life).

The excretory system removes waste products from the body, mainly through the kidneys, which filter blood to remove waste and excess water, producing urine. Humans normally have two kidneys, and each one contains roughly a million tiny filtering units called nephrons. The skin also plays a minor excretory role by releasing waste through sweat.

The endocrine system is your body's chemical messaging network, releasing hormones into the blood from glands to regulate processes like growth, metabolism, and mood. The pancreas releases insulin to control blood sugar, the thyroid gland in your neck controls metabolic rate, and the pituitary gland, tucked at the base of the brain, is often called the "master gland" because it controls the activity of several other glands in the body.

2. Common Diseases and Prevention

Diseases are broadly divided into two categories that exams love to test: communicable diseases, which spread from person to person through germs (bacteria, viruses, fungi, or parasites), and non-communicable diseases, which do not spread between people and are usually caused by lifestyle, genetics, or long-term conditions.

Communicable diseases spread through different routes. Diseases like the common cold, influenza, tuberculosis, and COVID-19 spread through the air, via droplets from coughing or sneezing. Diseases like cholera, typhoid, and hepatitis A spread through contaminated water or food. Diseases like malaria and dengue spread through mosquito bites, not directly between people.

Exam trap: A frequently confused pair is malaria and dengue, both spread by mosquitoes but by different species and with different symptoms. Malaria is caused by a parasite (Plasmodium) spread by the female Anopheles mosquito, and it typically causes cycles of high fever with chills. Dengue is caused by a virus spread by the Aedes mosquito (which typically bites during the day, unlike many other mosquitoes), and it causes high fever along with severe joint pain and a dangerous drop in platelet count. Remembering "Anopheles for malaria, Aedes for dengue" avoids this classic mix-up.

Vaccination is prevention's biggest success story and a heavily tested exam topic. A vaccine works by introducing a weakened or inactive form of a germ, or a harmless piece of it, into the body, training your immune system to recognise and fight that specific germ quickly if it shows up for real later. This is similar to a fire drill in a building — nobody gets hurt during the drill, but everyone learns exactly what to do so that a real fire causes far less damage. India's Universal Immunisation Programme covers diseases like tuberculosis (BCG vaccine), polio, diphtheria, pertussis (whooping cough), tetanus, measles, and hepatitis B for children.

Non-communicable diseases include conditions like diabetes, hypertension (high blood pressure), heart disease, and obesity, generally linked to diet, physical activity, stress, and genetics rather than germs. Diabetes occurs when the body cannot properly regulate blood sugar, either because the pancreas does not produce enough insulin (Type 1) or because the body's cells stop responding properly to insulin (Type 2, the far more common form, strongly linked to lifestyle). Hypertension is consistently high blood pressure in the arteries, which over years raises the risk of heart attack and stroke, and it is often called a "silent" condition because it frequently shows no obvious symptoms until real damage has already occurred.

Vitamin and mineral deficiency diseases are among the most repeated topics in SSC science sections, because they connect a nutrient directly to a visible disease.

Vitamin/Mineral	Deficiency Disease	Common Source
Vitamin A	Night blindness	Carrots, green leafy vegetables
Vitamin B1 (Thiamine)	Beriberi	Whole grains, legumes
Vitamin C	Scurvy (bleeding gums)	Citrus fruits like lemon, amla
Vitamin D	Rickets (weak bones in children)	Sunlight, eggs, fish
Vitamin K	Poor blood clotting	Green leafy vegetables
Iron	Anaemia (fatigue, paleness)	Spinach, jaggery, meat
Iodine	Goitre (swollen thyroid gland)	Iodised salt, seafood
Calcium	Weak bones and teeth	Milk, dairy products

Memory hook: Link Vitamin C to scurvy with "C for Citrus, Cures scurvy" — the same letter across all three words makes this pairing impossible to forget under exam pressure.

Exam trap: Vitamin D deficiency in children is called rickets, but the same deficiency in adults is called osteomalacia. SSC occasionally tests this adult-versus-child distinction, so do not answer "rickets" automatically if the question specifies adults.

Basic prevention habits worth remembering as a group: washing hands regularly prevents many communicable diseases, drinking clean or boiled water prevents cholera and typhoid, using mosquito nets and repellents prevents malaria and dengue, and a balanced diet with fruits, vegetables, grains, and dairy prevents most deficiency diseases. None of this needs deep medical knowledge, just the confidence to match cause with effect quickly under time pressure.

3. Plants Basics

Plants are the base of almost every food chain on Earth, and their most defining feature is that they can make their own food, a trait that makes them "producers" in ecological terms.

Photosynthesis is the process by which green plants make their own food using sunlight. It happens mainly in the leaves, inside tiny structures called chloroplasts, which contain a green pigment called chlorophyll. Chlorophyll absorbs sunlight energy and uses it to combine carbon dioxide (taken in from air through tiny pores on leaves called stomata) with water (drawn up from soil through roots) to produce glucose (a sugar, the plant's food and energy source) and oxygen (released back into the air as a byproduct).

In simple terms: Carbon dioxide + Water + Sunlight energy (captured by chlorophyll) → Glucose + Oxygen.

Memory hook: Think of a leaf as a tiny solar-powered kitchen. Sunlight is the electricity bill paid to run the kitchen, carbon dioxide and water are the raw ingredients bought from the market, chlorophyll is the chef who does the actual cooking, glucose is the meal the plant eats to grow, and oxygen is the kitchen's exhaust, released outward, which happens to be exactly what you and every other animal breathe in.

Exam trap: Photosynthesis happens only in the presence of sunlight, but plants also respire all the time, day and night, just like animals do, taking in oxygen and releasing carbon dioxide to release energy from glucose. Many students wrongly assume plants only "breathe out oxygen" and never take any in — in darkness, with no photosynthesis happening, a plant's respiration is the only gas exchange occurring, and it is taking in oxygen and releasing carbon dioxide during that time, same as you.

Plants have specialised parts, each with a clear job. Roots anchor the plant in soil and absorb water and minerals. Stems support the plant upright and transport water and nutrients between roots and leaves through internal tubes. Leaves are the primary site of photosynthesis. Flowers are the reproductive part of the plant, eventually producing seeds and fruit after pollination.

Two types of internal tubes run through a plant's stem, and SSC often tests the direction each one moves material. Xylem tissue carries water and dissolved minerals upward from the roots to the leaves. Phloem tissue carries the glucose made during photosynthesis (dissolved as sap) from the leaves down to other parts of the plant that need energy, like roots and growing fruit.

Memory hook: Remember direction with "Xylem gXoes uXp" — a small stretch, but pairing the letter X visually with the upward direction of water movement helps many students recall it correctly during the exam, since Xylem and Phloem are so easy to swap under pressure.

Exam trap: Xylem and phloem are among the most swapped terms in the whole biology syllabus. Xylem moves water upward (roots to leaves); phloem moves food, mainly glucose, both upward and downward depending on where it is needed, but its defining direction to remember for exams is carrying food away from the leaves where it was made.

Plants also need certain minerals from soil to grow well, similar to how your body needs vitamins. Nitrogen supports leaf growth and gives plants their green colour, phosphorus supports root development, and potassium supports overall plant health and disease resistance. This is exactly why fertiliser bags list an "NPK" ratio on the packaging, referring to these three key nutrients.

4. Basic Ecology and Environment

Ecology is the study of how living things interact with each other and with their physical surroundings. An ecosystem is any defined area where living organisms (plants, animals, microbes) interact with non-living factors (air, water, soil, sunlight) as a functioning unit — a pond, a forest, a garden, and even a fish tank are all examples of ecosystems at different scales.

Within an ecosystem, energy flows in a fixed direction through what is called a food chain. Producers (green plants) make their own food through photosynthesis and form the base of nearly every food chain. Primary consumers (herbivores, animals that eat only plants, like a goat or a deer) eat the producers. Secondary consumers (carnivores that eat herbivores, like a fox eating a rabbit) eat the primary consumers. Tertiary consumers or top predators (like a tiger or an eagle) sit at the very top, often with no natural predator of their own. Decomposers (bacteria and fungi) break down dead plants and animals, returning nutrients to the soil so the whole cycle can begin again.

Memory hook: Picture a village marketplace supply chain. The farmer growing crops is the producer. The local shopkeeper buying directly from the farmer is the primary consumer. The bigger wholesaler buying from several shopkeepers is the secondary consumer. The large city distributor at the very top of that chain is the tertiary consumer. And the sweeper who clears away spoiled, unsold produce at the end of each day, letting the market start fresh again, plays exactly the role of a decomposer.

Exam trap: A food chain is a single, straight-line sequence (grass → deer → tiger), while a food web is the more realistic, interconnected network of many overlapping food chains in the same ecosystem, since most animals eat more than one type of food and get eaten by more than one type of predator. If a question describes multiple interconnected chains, the correct term is food web, not food chain.

Biodiversity refers to the variety of life, plant and animal species, found in a particular region or across the planet. Regions with especially rich and unique biodiversity, under serious threat, are called biodiversity hotspots — India has notable ones including the Western Ghats and the Eastern Himalayas.

Environmental concerns commonly tested include:

Deforestation, the large-scale clearing of forests, reduces oxygen production, increases soil erosion since tree roots no longer hold soil in place, disturbs rainfall patterns, and destroys the habitat of countless species, pushing many toward extinction.

Pollution comes in several types your exam may distinguish between. Air pollution comes from vehicle exhaust, factory smoke, and burning of fossil fuels, and is linked to rising cases of respiratory illness in cities. Water pollution comes from untreated sewage, industrial waste, and agricultural chemicals draining into rivers and lakes. Soil pollution comes from excessive chemical fertilisers, pesticides, and improperly disposed waste.

Global warming refers to the gradual rise in Earth's average temperature, driven mainly by increasing levels of greenhouse gases, particularly carbon dioxide, methane, and water vapour, in the atmosphere. These gases trap heat from the sun that would otherwise escape back into space, working somewhat like a glass roof over a greenhouse used to grow vegetables in cold weather, which traps warmth inside to help plants grow even when it is cold outside — except at Earth's scale, this trapped heat is steadily raising global temperatures, melting glaciers, and shifting weather patterns. This overall effect of gases trapping heat is called the greenhouse effect, and a moderate natural greenhouse effect is actually essential for life, keeping Earth warm enough to sustain it; the problem tested by exams is the excess, human-caused intensification of this effect through burning fossil fuels.

Exam trap: Do not describe the greenhouse effect itself as inherently bad. A natural, moderate greenhouse effect keeps Earth's average temperature liveable; without any greenhouse effect at all, Earth would actually be far too cold to support life. Exams test whether you understand that it is the human-caused increase in greenhouse gases that is the real environmental problem, not the greenhouse effect's mere existence.

Conservation efforts commonly tested include afforestation (planting new trees, or restoring forest cover on previously deforested land), setting up wildlife sanctuaries and national parks to protect endangered species and their habitats, and rules around waste segregation and recycling to reduce landfill pollution. India has numerous well-known national parks and tiger reserves, such as Jim Corbett National Park (India's oldest national park, in Uttarakhand) and Kaziranga National Park in Assam, famous for its one-horned rhinoceros population.

Understanding these basics of the human body, disease prevention, plants, and ecology as connected, everyday knowledge, rather than isolated textbook facts, is exactly what turns biology into one of the fastest-scoring sections on your SSC MTS or CHSL paper.

Quick Revision — One-Line Facts

• Most nutrient absorption from digested food happens in the small intestine.
• The lungs exchange oxygen and carbon dioxide inside tiny air sacs called alveoli.
• The heart has four chambers and pumps blood through two loops, one to the lungs and one to the body.
• Arteries carry blood away from the heart; veins carry blood back toward it.
• Red blood cells carry oxygen; white blood cells fight infection; platelets help clotting.
• The cerebrum handles thinking and voluntary movement; the cerebellum handles balance; the medulla controls involuntary actions like heartbeat.
• Reflex actions, like pulling a hand away from heat, are controlled by the spinal cord for speed.
• An adult human skeleton has 206 bones; a newborn has around 300, which gradually fuse.
• Cardiac muscle works involuntarily and is found only in the heart.
• Kidneys filter blood and remove waste as urine, containing filtering units called nephrons.
• The pancreas releases insulin to regulate blood sugar levels.
• The pituitary gland is called the "master gland" for controlling other hormone glands.
• Communicable diseases spread between people; non-communicable diseases do not.
• Malaria spreads via the female Anopheles mosquito; dengue spreads via the Aedes mosquito.
• Vaccines train the immune system using a weakened or inactive form of a germ.
• Vitamin A deficiency causes night blindness; Vitamin C deficiency causes scurvy.
• Vitamin D deficiency causes rickets in children and osteomalacia in adults.
• Iron deficiency causes anaemia; iodine deficiency causes goitre.
• Photosynthesis uses sunlight, carbon dioxide, and water to produce glucose and oxygen.
• Chlorophyll, found in chloroplasts, is the green pigment that absorbs sunlight for photosynthesis.
• Plants respire all the time, taking in oxygen and releasing carbon dioxide, just like animals.
• Xylem carries water upward from roots to leaves; phloem carries food from leaves to other parts.
• Stomata are tiny pores on leaves that allow gas exchange.
• A food chain is a straight sequence of energy transfer; a food web links multiple food chains together.
• Decomposers, like bacteria and fungi, break down dead matter and recycle nutrients into soil.
• Biodiversity hotspots in India include the Western Ghats and the Eastern Himalayas.
• Global warming is driven by rising greenhouse gases like carbon dioxide and methane trapping heat.
• A moderate natural greenhouse effect is necessary for life; the excess human-made increase is the real problem.
• Afforestation and wildlife sanctuaries are key tools for environmental conservation.

Memory Tables

Table 1: Vitamin and Mineral Deficiency Diseases

Nutrient	Deficiency Disease	Key Symptom
Vitamin A	Night blindness	Difficulty seeing in dim light
Vitamin C	Scurvy	Bleeding gums
Vitamin D	Rickets (children) / Osteomalacia (adults)	Weak, soft bones
Iron	Anaemia	Fatigue, paleness
Iodine	Goitre	Swollen thyroid gland in neck

Table 2: Human Body Systems and Main Function

System	Main Organs	Main Function
Digestive	Stomach, small intestine, liver	Breaks down food, absorbs nutrients
Respiratory	Lungs, trachea	Exchanges oxygen and carbon dioxide
Circulatory	Heart, arteries, veins	Transports blood throughout the body
Nervous	Brain, spinal cord, nerves	Controls and coordinates body activity
Excretory	Kidneys	Filters blood, removes waste as urine

Table 3: Levels of a Food Chain

Level	Role	Example
Producer	Makes own food via photosynthesis	Grass, trees
Primary consumer	Eats producers	Deer, goat
Secondary consumer	Eats primary consumers	Fox, small carnivorous fish
Tertiary consumer	Top predator	Tiger, eagle
Decomposer	Breaks down dead matter	Bacteria, fungi

Practice MCQs

Q1. Most absorption of digested nutrients into the blood takes place in the: (a) Stomach (b) Small intestine (c) Large intestine (d) Oesophagus

Q2. Which blood component is mainly responsible for fighting infections in the body? (a) Red blood cells (b) Platelets (c) White blood cells (d) Plasma

Q3. Which vessels carry blood away from the heart? (a) Veins (b) Arteries (c) Capillaries (d) Nerves

Q4. Which part of the human brain controls balance and coordination? (a) Cerebrum (b) Cerebellum (c) Medulla oblongata (d) Spinal cord

Q5. How many bones are present in an adult human skeleton? (a) 186 (b) 206 (c) 226 (d) 300

Q6. Malaria is caused by a parasite transmitted through the bite of: (a) Aedes mosquito (b) Female Anopheles mosquito (c) Housefly (d) Tsetse fly

Q7. Deficiency of Vitamin C in the diet leads to which disease? (a) Rickets (b) Scurvy (c) Beriberi (d) Goitre

Q8. Which gland is often called the "master gland" of the human body? (a) Thyroid gland (b) Pancreas (c) Pituitary gland (d) Adrenal gland

Q9. Which pigment in plant leaves absorbs sunlight for photosynthesis? (a) Haemoglobin (b) Chlorophyll (c) Melanin (d) Carotene

Q10. What are the raw materials used by plants during photosynthesis? (a) Oxygen and glucose (b) Carbon dioxide and water (c) Nitrogen and water (d) Oxygen and water

Q11. Which plant tissue transports water and minerals from roots to leaves? (a) Phloem (b) Xylem (c) Stomata (d) Chlorophyll

Q12. In a grassland food chain of grass, deer, and tiger, the deer is classified as a: (a) Producer (b) Primary consumer (c) Secondary consumer (d) Decomposer

Q13. Organisms like bacteria and fungi that break down dead plants and animals are called: (a) Producers (b) Consumers (c) Decomposers (d) Predators

Q14. Which of the following gases is a major contributor to the greenhouse effect and global warming? (a) Nitrogen (b) Oxygen (c) Carbon dioxide (d) Argon

Q15. Vaccination protects the body from disease mainly by: (a) Killing all bacteria present in the body instantly (b) Training the immune system to recognise a specific germ (c) Replacing damaged cells with new ones (d) Increasing the number of red blood cells

Answer Key

Q	Answer	Reason
1	(b) Small intestine	This is where most digested nutrients pass into the bloodstream, aided by bile and enzymes.
2	(c) White blood cells	White blood cells form the body's defence system against infection; red cells carry oxygen instead.
3	(b) Arteries	Arteries always carry blood away from the heart, while veins carry it back toward the heart.
4	(b) Cerebellum	The cerebellum specifically manages balance and coordinated movement, distinct from the thinking cerebrum.
5	(b) 206	An adult skeleton has 206 bones, fewer than a newborn's roughly 300 because bones fuse with growth.
6	(b) Female Anopheles mosquito	This specific mosquito species transmits the Plasmodium parasite that causes malaria.
7	(b) Scurvy	Vitamin C deficiency causes scurvy, marked by bleeding gums and weakness.
8	(c) Pituitary gland	It regulates the activity of several other endocrine glands, earning the "master gland" title.
9	(b) Chlorophyll	Chlorophyll is the green pigment in chloroplasts that captures sunlight energy for photosynthesis.
10	(b) Carbon dioxide and water	These two, combined using sunlight energy, are converted into glucose and oxygen.
11	(b) Xylem	Xylem tissue moves water and dissolved minerals upward from roots to leaves.
12	(b) Primary consumer	The deer eats the producer (grass) directly, making it a primary consumer in the chain.
13	(c) Decomposers	Decomposers break down dead organic matter and return nutrients to the soil.
14	(c) Carbon dioxide	Carbon dioxide is a major greenhouse gas that traps heat and drives global warming.
15	(b) Training the immune system to recognise a specific germ	Vaccines expose the body to a weakened or inactive germ so it can respond quickly to the real infection later.